Supply device for a motor vehicle alternator, and alternator employing such a device

ABSTRACT

An electrical supply device includes a set of armature coils which are coupled together in a polygonal mode. The coils are connected to a single bridge rectifier which includes a set of controllable elements allowing switching between a first operating mode in which some of the coils are electrically connected in series and a second operating mode in which all of the coils are electrically connected in parallel. An alternator for a motor vehicle includes the disclosed supply device.

This invention relates to the field of motor vehicle alternators andmore particularly a power supply device and the operating modes whichare associated with it for such alternators. It also extends to analternator comprising such a power supply device and employing suchoperating modes.

In a conventional manner, an alternator fitted to a motor vehiclecomprises a stator in which is placed a rotor, a shaft of which isrotationally driven by the vehicle's internal combustion engine by meansof an appropriate device. In a manner which is also conventional, thestator comprises at least two armature windings connected to arectification device to form two power supply sources.

As a result of the method of driving the rotor, the performance of suchan alternator varies with the speed of the internal combustion engine.However, the vehicle's own systems need a power supply of constantvoltage.

In order to remedy this drawback, it is known, in particular, for twoindependent three-phase windings to be made at the stator and for anelectronic circuit to be added, connecting the said windings, making itpossible, depending on the speed of the vehicle's internal combustionengine, to connect the said windings in series or in parallel. Moreprecisely, the said connecting electronic circuit makes a seriesconnection of the said windings when the engine speed is low in order toobtain a high off-load voltage and high current at low speed at thealternator output and a parallel connection in the case of high speed ofthe said internal combustion engine, in order to increase the currentdelivered by the said alternator.

In a known manner, each of the three-phase windings is associated with adiode rectification device and several solutions are known in the priorart for making the above-mentioned connecting electronic circuit. Forexample, document FR2807232 proposes associating each of the dioderectification devices of the two three-phase windings with an auxiliarybridge rectifier also made up of diodes and connecting the saidauxiliary bridge rectifiers by switchable means such as, but withoutbeing restricted to, a transistor, controlled diode or a switch.Document U.S. Pat. No. 6,005,786, for its part, proposes placing thefollowing directly at the outputs of the two three-phase windings, eachassociated with its rectification device: a set of switchable means withwhich it is possible to interconnect some of the outputs of the saidwindings, depending on the number and nature of the switchable meansactivated.

Even if, with these coupling modes, it is possible to obtainsatisfactory alternator performance, the said coupling modesnevertheless involve the use of a relatively large number of electroniccomponents, which increases the alternator's overall dimension. As, on amotor vehicle, the alternator is located in a restricted space, theconstraints linked with its overall dimension also involve the saidelectronic components' being relatively close to one another. As aresult, it is then necessary to add a set of means with which thethermal dissipation of the calories emitted during operation can takeplace (fans, liquid circulation cooling devices, etc.), which increasesthe complexity of the alternator and therefore its cost.

The aim of this invention is to propose a rectification device for analternator intended for a motor vehicle, in which the number ofelectronic components is small, whereby the overall dimension of thesaid alternator can be reduced, while high performance is retained interms of voltage and current delivered, irrespective of the speed of thevehicle's internal combustion engine.

With this aim, the principal object of this invention is a power supplydevice, particularly for a motor vehicle's own system, characterised inthat it comprises a set of armature coils assembled in a polygonalcoupling mode and in that the said coils are connected to a singlebridge rectifier comprising a set of controllable elements with whichswitching can be carried out between a first operating mode in whichsome armature coils are electrically connected in series and a secondoperating mode in which all of the said armature coils are electricallyconnected in parallel.

According to a preferred embodiment of the invention, the power supplydevice comprises six armature coils, assembled in hexagonal coupling. Inthe following, the invention will be preferentially described accordingto this preferred but not exclusive embodiment.

In this preferred embodiment, according to a feature of the invention,the controllable elements of the rectification device are made up of aset of six thyristors and are placed at the terminals of the armaturecoils alternately with a set of diodes. More precisely, according to anadvantageous embodiment of the invention, one of the terminals of eachof the armature coils is connected to a set of two thyristors, the otherterminal being connected to a set of two diodes.

According to another feature of the invention, the said terminal of eachof the armature coils connected to the said two thyristors is connectedto the anode of one of them, then named a positive thyristor and to thecathode of the other one, therefore named a negative thyristor. The sameapplies to the above-mentioned sets of two diodes, each of which is thusformed from a so-called positive diode as it is connected through itsanode to the armature coil and from a so-called negative diode as it isconnected through its cathode to the said coil.

Advantageously, the anodes of the various different so-called negativerectification elements are connected to earth and the cathodes of thevarious different so-called positive rectification elements areconnected to the power supply line of the motor vehicle's own system.

It follows from the foregoing that, when the switchable elements (here,the thyristors) are not activated, the armature coils are connected inseries, two by two. Taking into account the existing time phase shift of120 degrees, due to the hexagonal coupling, between two consecutivecoils, the set therefore delivers an electromotive force equal to theelectromotive force delivered by one of the coils multiplied by a factorequal to the square root of three. In the event that the armature coilsare made up of N turns, everything therefore happens as if the saidcoils comprised a greater number of turns; more precisely, the powersupply device according to the invention behaves as if its armaturecoils were formed from N×√3 turns. Consequently, the power delivered bythe power supply device according to the invention is greater than thepower which the same device would deliver if the armature coils whichform it comprised N turns. In the context of the application of theinvention to making an alternator for a motor vehicle, this situationwill be sought for the low speeds of internal combustion engineoperation, speeds for which, with the invention, it will be possible toobtain a greater current for low rotor rotation speeds.

Conversely, when the switchable elements (here, the thyristors) areactivated, the armature coils of the power supply device according tothe invention are electrically connected in parallel; with this, it ispossible to increase the total current delivered. In the context of theapplication of the invention to making an alternator for a motorvehicle, this situation will be rather sought for the high speeds ofinternal combustion engine operation, speeds for which, with theinvention, it will be possible to obtain a greater current at thealternator output.

With the invention, due to the polygonal coupling of the armature coilsand the putting in place of controllable rectification elements such asthyristors, it is possible to make a simple power supply device withwhich there can be rapid switching between a state in which it deliversa high voltage and a state in which it delivers a high current, whileemploying a single rectification device made up of a smaller number ofelements than the rectification devices conventionally used forachieving the same aim.

With the invention, applied to the field of alternators for motorvehicles, it is therefore possible, through the reduction in the numberof components necessary for rectification, to reduce the overalldimension of the alternator obtained, while having at one's disposal asystem having high performance through the switching between the“series” state and the “parallel” state of the armature coils. Withthis, it is also possible to reduce the number of turns forming the saidarmature coils, while maintaining a high level of performance,irrespective of the engine operating speeds.

With this, it is also possible, through the reduction in the number ofrectification components, to simplify the thermal dissipation deviceassociated with these and finally it is possible, due to the simplicityof operation of its rectification device, to use lower-cost standardcomponents.

In the final analysis, with the invention, it is therefore possible tomake an alternator which is more compact, simpler and therefore lessexpensive than the alternators known in the prior art, yet havingperformance at least as high as these latter and even—particularly forthe vehicle engine's low speeds—higher than these.

It is to be noted that the number of controllable elements of therectification device is not limited to the number which has just beenmentioned and that, depending on variants, this number can, inparticular, be smaller, as will be explained below. Similarly, thearrangement described above for the said rectification elements is notexclusive, as will also be set out below.

Other features and advantages of the invention will appear when thefollowing description is read, with reference to the followingillustrations in which:

FIG. 1 is a schematic representation of a preferred embodiment of apower supply device according to the invention,

FIG. 2 is a curve showing, as a function of the speed of a motorvehicle's internal combustion engine, the current delivered by analternator comprising a power supply device according to the invention,

FIG. 3 is a schematic representation of an alternative embodiment of theinvention,

FIG. 4 is a perspective schematic view of the rear part of an alternatoremploying a power supply device according to the invention and

FIG. 5 shows a controllable element with MOSFET transistors.

According to the preferred embodiment of the invention shown in FIG. 1and referred to above, the power supply device according to theinvention comprises six coils numbered 1 to 6 and connected to oneanother in hexagonal coupling; the output terminal of coil 1 is thusconnected to the input terminal of coil 2, the output terminal of whichis connected to the input terminal of coil 3 and so on, the outputterminal of coil 6 being connected to the input terminal of coil 1. Itshall be presumed in the following that each of the coils 1 to 6comprises N turns, it being possible for each of the N turns to beformed, in a known manner, from any predefined number of conductingwires.

According to the invention, the set formed by the coils 1 to 6 isassociated with a single rectification device comprising a set ofcontrollable elements.

According to the preferred embodiment of the invention shown in FIG. 1,this rectification device comprises a set of thyristors T forming theset of controllable elements and a set of diodes D, the number andarrangement of which will now be described.

In a variant, the controllable elements can be formed from or comprisetransistor switching elements, particularly of the MOSFET type, as shownin FIG. 5. These transistor switching elements can advantageouslyreplace thyristors in some applications of the invention.

As shown in FIG. 1, there are six thyristors T, grouped in pairs T1, T2and T3. The same applies to the diodes D, of which there are also six,grouped in pairs D1, D2 and D3. According to the non-limiting, preferredembodiment of the invention shown in FIG. 1, the diodes of the pairs D1,D2 and D3 are Zener diodes in order to ensure the system protectionfunction.

According to the invention, the pairs of thyristors T and pairs ofdiodes D are placed alternately at the terminals of coils 1 to 6, asFIG. 1 shows. Thus, each of the said coils 1 to 6 is connected, throughone of its terminals, to a pair of thyristors T and, through its otherterminal, to a pair of diodes D.

More precisely, with reference to coil 1 for example, the terminalconnected to the pair of thyristors T1 is connected, on one hand, to theanode of one of the said thyristors, consequently named a positivethyristor and referenced T1+ in FIG. 1 and, on the other hand, to thecathode of the other thyristor of the said pair T1, consequently named anegative thyristor and referenced T1− in FIG. 1. The same applies to thepair of diodes D1 connected to the other terminal of the said coil 1;the said terminal of the said coil 1 is thus connected to the anode ofone of the diodes D1 or positive diode designated by the reference D1+and to the cathode of the other diode D1 or negative diode designated bythe reference D1−.

This is so for the set of coils 1 to 6. The rectification device of thepower supply device according to the invention is thus made up of twosub-sets of so-called “positive” or “negative” components, as they areconnected through their anodes or through their cathodes, respectively,to the terminals of the said coils.

Advantageously and as FIG. 1 shows, the anodes of the components of the“negative” sub-set are connected to earth and the cathodes of thecomponents of the “positive” sub-set are connected to a power supplyline, for example the power supply line of a motor vehicle's own system.

When the thyristors T1, T2 and T3 are not activated, the coils 1 and 2are electrically connected in series, as well as coils 3 and 4 and coils5 and 6. Consequently, the electromotive force generated by the powersupply device according to the invention is equal to the vector sum ofthe electromotive force generated by each of the coils connected inseries. As these coils are successively shifted, two by two, by 120degrees taking into account the hexagonal assembly chosen, the totalelectromotive force generated by the power supply device according tothe invention is equal to the electromotive force generated by one ofthe coils, multiplied by a factor equal to the square root of three. Ifeach coil is, as has been stated above, made up of N turns, theperformance of the device according to the invention will therefore beequal to that of a conventional device made up of coils formed from Ntimes the square root of three turns (N×√3).

With equal performance, by means of the device according to theinvention, it is possible to reduce the number of turns per coil andthus to increase the power of the machine with equal volume.

When the thyristors of the pairs T1, T2 and T3 are activated, the coils1 to 6 are electrically connected in parallel. Consequently, theelectromotive force generated by the device according to the inventionis equal to that generated by each coil and the current delivered by thesaid device is increased. The performance of the device according to theinvention is, here, that of a device formed from coils of N turns placedin parallel.

These phenomena are illustrated in FIG. 2, which shows the currentdelivered by an alternator as a function of the number of revolutionsper minute of the internal combustion engine to which it is fitted.

Curve I, in a broken line, shows the current delivered by an alternatoras conventionally known in the prior art, comprising two three-phasewindings of six turns each, connected in series by means of one of thedevices referred to at the beginning of this document. Curves II andIII, in an unbroken line and in a dot-and-dash line respectively, showthe performance of an alternator comprising a power supply deviceaccording to the invention, the coils of which comprise 5 turns, in itsdifferent operating modes.

More precisely, curve II shows the current delivered by means of adevice according to the invention when the pairs of thyristors T1, T2and T3 are not activated, i.e. when coils 1 and 2, 3 and 4 and 5 and 6respectively are electrically connected in series, two by two. Itclearly appears that, at low engine speed, the performance of the deviceaccording to the invention is higher than that of the device in whichthe windings comprise 6 turns. It is even to be noted that, at around2,000 revolutions per minute, which corresponds to the engine idlespeed, the current delivered by the alternator equipped with the deviceaccording to the invention is greater than that supplied by a device inwhich the windings comprise 6 turns.

Therefore, with the invention, it is possible, in the case of low enginespeeds, to make an alternator having performance which is at least equalto or even higher than that of a device in which the windings comprise agreater number of turns.

Curve III, in a dot-and-dash line in FIG. 2, shows the current deliveredby means of a device according to the invention when the pairs ofthyristors T1, T2 and T3 are activated. As has been explained above, thecoils 1 to 6 are then electrically connected in parallel. Consequently,there is an appreciable increase in the current delivered by thealternator fitted with such a device. This is particularly visible inFIG. 2, in the case of high engine speeds, in comparison with thecurrent delivered by the conventional alternator, the characteristiccurve of which is shown by curve I.

With the device according to the invention, it is thus possible toobtain—by simple activation of the three pairs of thyristors T1, T2 andT3—two operating modes, due to which the alternator of a motor vehiclecomprising the said device has high performance, for a reduced number ofcoil turns.

The weight of such an alternator can thus be reduced, whichproportionately reduces its energy cost on the vehicle. Similarly, therectification set—single and formed from only 6 thyristors and 6diodes—is simplified due to the device according to the invention, incomparison with the bridge rectifiers used at present. Consequently, theoverall dimension of an alternator comprising the device according tothe invention can be reduced further and the compactness of the saidalternator can, moreover, also be increased by means of a simplificationof the device for thermal dissipation of the calories emitted by thecomponents of the rectification set, these being fewer in comparisonwith the alternators known at present.

FIG. 4 shows a foreseeable embodiment for an alternator comprising adevice according to the invention.

The latter illustration shows the positive dissipater 10 and negativedissipater 11 of an alternator as known in the prior art, on which areconventionally placed the rectifier diode bridges at the locationsreferenced by D+ and D− respectively.

In an alternator employing the device according to the invention in itspreferred embodiment described above, the thyristors T1+, T2+ and T3+take the place of three of the diodes D+ and the thyristors T1−, T2− andT3− take the place of three of the diodes D−. Therefore, thyristors anddiodes adjoin on the positive and negative dissipaters and—due to theabsence of any complementary connection electronic circuit—thecompactness of the set can be improved.

It is to be noted that the invention is not limited to the embodimentwhich has just been described and that it extends, in particular, to anyvariant, in particular any variant employing equivalent means or anytechnically operating combination of these.

Thus, for example, the number of pairs of thyristors, established atthree in the embodiment which has just been described, can beestablished at four in an alternative embodiment of the invention, shownin FIG. 3.

According to this alternative embodiment, four pairs of thyristors T1,T2, T3 and T4, are placed at the terminals of coils 1 to 6, alternatingwith two pairs of diodes D1 and D2.

More precisely, coil 1 is connected, through one of its terminals, to apair of thyristors T1 and, through its other terminal, to a pair ofdiodes D2. Coil 2 is, for its part, connected through one of itsterminals to the said pair of diodes D2 and, through its other terminal,to a pair of thyristors T2. Coil 3 is connected through each of itsterminals to two pairs of thyristors, T2 and T3 respectively, whereascoil 4 is connected, through one of its terminals, to the saidthyristors T3 and, through its other terminal, to the second pair ofdiodes D2. Coil 5 is then connected to the said diodes D2 and to thethyristors T4 respectively, coil 6 being connected to the saidthyristors T4 and to the thyristors T1 mentioned above.

When the thyristors T1, T2, T3 and T4 are not activated, coils 2, 3 and4 on one hand and 5, 6 and 1 on the other hand are electricallyconnected in series. In a manner similar to that which has been referredto above, this will lead, for a given number of turns in coils 1 to 6,to an increase in the current delivered by an alternator comprising sucha device, in particular at low engine speeds of the vehicle concerned.When the thyristors T1, T2, T3 and T4 are activated, coils 1 to 6 areelectrically connected in parallel as above.

Therefore, due to the invention, it is possible to make a power supplydevice and vehicle alternator which are simple and compact and lessexpensive than the devices and alternators known at present, whilemaintaining high levels of performance.

It is also to be noted that if, according to the embodiments of theinvention shown in the illustrations, diodes D1, D2 and D3 are Zenerdiodes, the latter can be replaced with standard diodes—costing less—andperform the system protection function through an external device.

Finally, it is to be clearly stated that, to respond to specificoperating constraints, it is possible to consider making the deviceaccording to the invention by using eight, ten or twelve coils assembledin octagonal, decagonal or dodecagonal coupling modes respectively. Inthese cases, according to preferred embodiments of the invention, thecontrollable elements of the rectification device will advantageouslycomprise four, five or six pairs of thyristors placed alternating withthe same number of pairs of diodes at the terminals of the said coils,in order to obtain an operating mode in which the said coils will beelectrically connected in series, two by two.

1. A power supply device, particularly for a motor vehicle's own system, characterized in that it comprises a set of armature coils assembled in a polygonal coupling mode and in that the coils are connected to a single bridge rectifier comprising a set of controllable elements with which switching can be carried out between a first operating mode in which some armature coils are electrically connected in series and a second operating mode in which all of the said armature coils are electrically connected in parallel.
 2. A device according to claim 1, characterized in that there are six armature coils (1, 2, 3, 4, 5 and 6) and in that these are assembled in a hexagonal coupling mode.
 3. A device according to claim 1, characterized in that the controllable elements comprise thyristors.
 4. A device according to claim 3, characterized in that the thyristors are assembled in three pairs (T1, T2 and T3) connected to the terminals of the coils (1, 2, 3, 4, 5 and 6) alternating with three pairs of diodes (D1, D2 and D3), in such a way that, in the absence of activation of the thyristors (T1, T2 and T3), the coils are electrically connected in series, two by two.
 5. A device according to claim 4, characterized in that each of the coils (1, 2, 3, 4, 5 and 6) is connected, through one of its terminals, to the anode of one of the diodes of the pairs of diodes (D1, D2 and D3) and to the cathode of the other diode of the pair (D1, D2 and D3) respectively and—through its other terminal—to the anode of one of the thyristors of one of the pairs of thyristors (T1, T2 and T3) and to the cathode of the other thyristor of the pair (T1, T2 and T3) respectively, the anodes of the thyristors or diodes connected through their cathodes to the coils being connected to earth and the cathodes of the thyristors and diodes connected through their anodes to the coils being connected to the power supply line of the vehicle's own system.
 6. A device according to claim 1, characterized in that the thyristors are assembled in four pairs (T1, T2, T3 and T4) and the device comprises diodes which are assembled in two pairs (D1 and D2), the thyristors (T1, T2, T3 and T4) and the diodes (D1 and D2) being connected to the terminals of the coils (1, 2, 3, 4, 5 and 6) in such a way that, in the absence of activation of the thyristors, the coils are electrically connected in series, three by three.
 7. A device according to claim 3, characterized in that the thyristors are replaced partially or totally with transistor controllable elements.
 8. An alternator for a motor vehicle, characterized in that it comprises a power supply device according to claim
 1. 9. An alternator according to claim 8, characterized in that positive controllable elements, connected through their anodes to the coil terminals, are placed, as well as the other elements of the power supply device connected through their anodes to the coils, on a dissipater connected to a power supply line of the vehicle and in that negative controllable elements, connected through their cathodes to the coil terminals, are placed, as well as the other elements of the power supply device connected through their cathodes to the coils, on a dissipater connected to the vehicle's earth. 